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High speed spindles are used today in many manufacturing operations. They may be integrated into a CNC machining center or installed in a special machine. When properly used, a high speed spindle can reduce cycle time, improve part quality and boost efficiency. However, when used improperly, a high speed spindle can turn into a hot mess, literally. Here are some problem areas to avoid:
A cutting tool is designed to slice material from a piece of raw stock and produce a finished part. The cutter design assumes the proper feeds and speeds will be used. If they are not, problems will arise.
For example, if you are cutting a hard material (think mold & die) and get too aggressive with depth of cut or feed rate, the cutter will be slicing more material than it is designed to do. This will result in excessive axial loading and heating of the cutter.
Excessive heating can adversely affect surface finish quality, as well as create metallurgical changes in the cutter material. This can cause the cutter to rapidly wear or even fracture. The sharp cutting edges can become very hot and break down, making the problem worse.
The solution? Use the right cutting tool. Follow the recommended feeds, RPM and depth of cut, especially for hard materials. Start on the conservative side and progress carefully. Consider coatings. All of this will help ensure the best outcome.
Milling power has a direct relation to the material volume removal rate. Let’s consider a typical aircraft grade aluminum, 6061-T6. For every cubic inch per minute of material removed, you need 1/4 horsepower from your spindle motor. And, if we follow reasonable cutting parameters for this material, and a 1”, 2 flute cutter, running at 30,000 RPM, we’ll need about 75 HP! Probably way more than we have available from our spindle. So, let’s back off on the cutter diameter and go to ½”. That only reduces the power to 35 HP. We can reduce the feed rate, but, at some point, the chip thickness becomes too thin and we start to create surface finish issues.
As you can see, cutting soft materials can get complex. Better to plan ahead. Knowing your spindle HP capacity can lead you to select the best size cutter, RPM and number of flutes. Once you have selected the cutting parameters, you can lower the amount of power required by reducing the depth of cut per pass. More passes at a lower DOC. This will maintain the best chip thickness and material removal without overloading your spindle motor.
It is also important to consider chip flow and coolant through the cutter flutes. Use cutters designed for high speed milling. Excessive chip flow, without sufficient cutting fluid and clearance, can cause build-up in the flutes and on the cutting edges. It wastes power and produces a lousy surface finish.
The most common cause of destructive vibration is poor cutting parameters. Incorrect feeds, speeds and depth of cut variables create a poor cutting process. A poor process wastes money.
Another common cause of vibrations is the use of long cutting tools at high RPM. At high speeds, long tools can actually bend and “whip”. This creates run out and vibrations. This is not good. However, sometimes it is necessary to use a long tool to reach a part feature that must be cut. So, to solve this problem, you may have to slightly reduce the RPM and feeds for this tool to eliminate the vibration. Precision and control really count here, so make sure you are using the most accurate tool clamping collet for that tool.
No, not always. As listed above, a high speed cutting process, to be the most effective, must be optimized. Optimizing a process includes changing variables until you achieve the best results. This means finding the best cutting tool, coolant, RPM, feed rate and depth of cut that maximizes part quality and minimizes cycle time. This usually does not include running the spindle at full speed, unless it fits the process.
Remember, running a high speed spindle at full speed maximizes the stress on the spindle bearings, effectively minimizing the bearing life.
Running at full RPM can also maximize the level of tool vibration due to cutting chatter or tool imbalance.
How do you know when your process has been fully optimized? High quality parts are coming out. Spindle life is reasonable. Cutting tool life is as predicted. Vibration levels are low. It will take some work to get there, but, in the end it is well worth it!
Overworking the Cutting Tool
A cutting tool is designed to slice material from a piece of raw stock and produce a finished part. The cutter design assumes the proper feeds and speeds will be used. If they are not, problems will arise. For example, if you are cutting a hard material (think mold & die) and get too aggressive with depth of cut or feed rate, the cutter will be slicing more material than it is designed to do. This will result in excessive axial loading and heating of the cutter.
Excessive heating can adversely affect surface finish quality, as well as create metallurgical changes in the cutter material. This can cause the cutter to rapidly wear or even fracture. The sharp cutting edges can become very hot and break down, making the problem worse.
The solution? Use the right cutting tool. Follow the recommended feeds, RPM and depth of cut, especially for hard materials. Start on the conservative side and progress carefully. Consider coatings. All of this will help ensure the best outcome.
Overloading the Spindle Motor
High speed spindles have the ability to remove material at very high rates of volume, especially soft materials like aluminum or plastics. Many aircraft components require the removal of as much as 90% to get to a finished part. So, it is critical to keep in mind how material removal relates to spindle power.Milling power has a direct relation to the material volume removal rate. Let’s consider a typical aircraft grade aluminum, 6061-T6. For every cubic inch per minute of material removed, you need 1/4 horsepower from your spindle motor. And, if we follow reasonable cutting parameters for this material, and a 1”, 2 flute cutter, running at 30,000 RPM, we’ll need about 75 HP! Probably way more than we have available from our spindle. So, let’s back off on the cutter diameter and go to ½”. That only reduces the power to 35 HP. We can reduce the feed rate, but, at some point, the chip thickness becomes too thin and we start to create surface finish issues.As you can see, cutting soft materials can get complex. Better to plan ahead. Knowing your spindle HP capacity can lead you to select the best size cutter, RPM and number of flutes. Once you have selected the cutting parameters, you can lower the amount of power required by reducing the depth of cut per pass. More passes at a lower DOC. This will maintain the best chip thickness and material removal without overloading your spindle motor.
It is also important to consider chip flow and coolant through the cutter flutes. Use cutters designed for high speed milling. Excessive chip flow, without sufficient cutting fluid and clearance, can cause build-up in the flutes and on the cutting edges. It wastes power and produces a lousy surface finish.
Excessive Vibrations can Damage Spindles
The Beach Boys had a song about “Good Vibrations”. Unfortunately, it does not apply to spindles. As noted in previous blog articles, excessive vibrations can be very damaging to the spindle bearings, tooling systems and part quality.The most common cause of destructive vibration is poor cutting parameters. Incorrect feeds, speeds and depth of cut variables create a poor cutting process. A poor process wastes money.Another common cause of vibrations is the use of long cutting tools at high RPM. At high speeds, long tools can actually bend and “whip”. This creates run out and vibrations. This is not good. However, sometimes it is necessary to use a long tool to reach a part feature that must be cut. So, to solve this problem, you may have to slightly reduce the RPM and feeds for this tool to eliminate the vibration. Precision and control really count here, so make sure you are using the most accurate tool clamping collet for that tool.
Faster is Not Always Better for Spindles!
On many occasions I have visited customers using IBAG high speed spindles. They are having challenges, and need some help sorting them out. Often, I find the spindle always running at the maximum RPM! Why? They seem to think, “I have a 30K spindle, why not run it at maximum speed? Isn’t that how I get the maximum benefit?No, not always. As listed above, a high speed cutting process, to be the most effective, must be optimized. Optimizing a process includes changing variables until you achieve the best results. This means finding the best cutting tool, coolant, RPM, feed rate and depth of cut that maximizes part quality and minimizes cycle time. This usually does not include running the spindle at full speed, unless it fits the process.Remember, running a high speed spindle at full speed maximizes the stress on the spindle bearings, effectively minimizing the bearing life.
Running at full RPM can also maximize the level of tool vibration due to cutting chatter or tool imbalance.
How do you know when your process has been fully optimized? High quality parts are coming out. Spindle life is reasonable. Cutting tool life is as predicted. Vibration levels are low. It will take some work to get there, but, in the end it is well worth it!
Contact IBAG for High Speed Spindles Today
For more information regarding our high speed spindle options, get a quote or contact IBAG today! IBAG is your trusted source for high speed micro spindles and fully automatic CNC spindle control conversion systems.
